Synthesis of porous composite material at combustion of titanium and boron powders and nickel-clad aluminum granules

Abstract

Self-propagating high-temperature synthesis (SHS) was carried out in the Ni-Al-Ti-B system. The aim of the study was to obtain a composite material with ceramic and intermetallic frameworks and with a developed porous structure in the combustion mode in one process step from the «boron-titanium-large nickel-clad aluminum granules» powder system pressed by sequential batch compaction. The synthesis process featured by a stage nature where a highly exothermic reaction between titanium and boron formed a boride matrix with developed open porosity and acted as a «chemical furnace» to maintain the reaction in clad granules resulting in nickel aluminides. The aluminide melt impregnated the porous diboride matrix. The synthesis stages are reflected in the process thermograms. The final structure of the product features multi-scale porosity characterized by large round pores (~100÷160 μ m in diameter) with the location corresponding to the position of clad granules in the original powder system. Small (0.1-5.0 μ m) and some average-sized (up to 15 μ m) diboride matrix pores are filled with nickel aluminides. The resulting material has a composite structure in analogy with interpenetrating frameworks - ceramic (TiB 2 ) and aluminide (NiAl, Ni 3 Al). The diboride matrix is formed by randomly oriented small hexagonal crystals with a size of mainly ~0.2÷1.0 μm across. Diboride crystalline grains increase in size to 2-6 um in diameter and 0.5-2.0 μm in thickness near the macropores becoming strongly plate-shaped. The main size of intermetallic layers filling the pores between the diboride crystalline grains is ~0.2÷1.0 μm.